Many compounds are irritating or painful when contacted with bodily surfaces. Examples include urushiols, which are constituents of poison oak, poison ivy, poison sumac, and other oily plant resins with irritating properties. Another example is capsaicin. Capsaicin is a constituent of pepper sprays, and capsaicin and its analogs are used in topical form for pain relief. Even at low concentrations (e.g., 0.075% by weight) capsaicin preparations can cause burning pain and hyperalgesia. This is the effect sought in pepper sprays, and is a side effect of therapeutic treatments of pain. At higher capsaicin concentrations used for the treatment of some intractable pain conditions, the initial pain accompanying application of capsaicin is treated by anesthesia (see, e.g., U.S. Pat. Nos. 6,248,788 and 6,239,180).